Biotic modifiers are species that strongly alter environmental conditions, and that often shape local communities. When more than one biotic modifier co-occurs, the potential for interactive effects exists, where the effects of one species may negate or enhance the impacts of a second biotic modifier. Here we test for an interactive effect of aardvark (Orycteropus afer) burrows and tree presence on soil (soil temperature, moisture and compaction) and understorey vegetation properties (plant cover, species richness and composition) in a semi-arid savannah. Aardvark burrowing altered abiotic conditions, with soil temperature and compaction being lower, and soil moisture higher, in burrow entrances than at the burrow mounds and control microsites. In addition, the impact of aardvark burrowing on soil moisture and soil compaction was mediated by the occurrence of trees. In contrast, vegetation cover and species richness were independently affected by burrowing and trees, while vegetation composition was only affected by the occurrence of trees, but not by burrowing. This research suggests that co-occurring biotic modifiers can have both independent and interactive effects, and disentangling their impacts will help understand the mechanisms underlying dryland plant communities.

生物修饰剂是会强烈改变环境条件并经常塑造当地社区的物种。当同时出现一种以上的生物修饰剂时，存在相互作用的可能性，其中一种物种的作用可能抵消或增强另一种生物修饰剂的影响。在这里，我们测试土豚的互动效应（Orycteropus AFER）在半干旱大草原上的土壤和土壤（土壤温度，湿度和压实度）和地下植被特性（植物覆盖度，物种丰富度和组成）上有洞穴和树木。与洞穴土丘和对照微地点相比，洞穴入口处的土豚挖穴改变了非生物条件，土壤温度和压实度较低，土壤水分较高。此外，土豚挖穴对土壤水分和土壤压实的影响是通过树木的发生来介导的。相反，洞穴和树木独立地影响了植被的覆盖率和物种丰富度，而植被的构成仅受树木的发生而不受洞穴的影响。这项研究表明，共同存在的生物修饰剂可以同时具有独立和交互作用，